Devices for saving or limiting the rate of flow of fluids such as water are well known in the art. Said devices are widely used to restrict fluid flow in showers, faucets, lavatories, toilets, etc. and particularly comprise a connecting tube which is provided with an inlet portion having internal threads and with an outlet portion having external threads, the portion corresponding to the external threads being of a smaller diameter than the remainder of the body of the connecting tube, said connecting tube being provided with a helical spring of a shape and a strength suitable to allow the desired rate of flow and arranged within said tube, and a specially designed needle-type shutter, particularly of a stepped cylindrical shape, concentrically arranged within said spring such that at the inlet end of the shutter, there is formed a flange, on the internal part of which bears the spring surrounding the needle type shutter, said spring bearing at its lower portion on an internal shoulder formed in the connecting tube.
The above mentioned flange arranged on the upper end of the needle type shutter, is provided with one or a plurality of axially extending holes for permitting the fluid to flow therethrough. During the operation of the prior art fluid rate of flow limiting devices, the vibration of the shutter due to passage of the fluid, produces a rattling effect of the body ends of the needle type shutter against the internal wall of the connecting tube and produces a noise level which may be regarded as being of a high degree of annoyance. On the other hand, the holes provided for the passage of the fluid, are rapidly clogged and even completely obstructed in a relatively short period of time, particularly when the fluid is impure or hot water. The above defects cause significant inconveniences because of the annoying noise of said prior art devices and because of the cumbersome and costly operation of frequently disassembling said connecting tube in order to clean the fluid flow holes of the shutter.
U.S. patent application Ser. No. 07/360,815 filed on June 2, 1989 by the same applicant hereof, now U.S. Pat. No. 4,962,792 describes and illustrates a device for restricting the flow rate of fluids, which represents a considerable advance over the prior art existing devices, inasmuch as by very simple means, said device eliminates the noise and the rattling effect produced by the vibration of the needle-type shutter of the prior art. The device of U.S. Ser. No. 07/360,815, now U.S. Pat. No. 4,962,792 comprises a needle-type shutter slidably movable within a tubular fitting towards and away from a flow restricting assembly comprising an annular soft washer sandwiched between a pair of hard washers, said soft washer having an opening of a diameter smaller than said hard washers, within which a reduced diameter stem portion is received when the fluid pressure biases the shutter towards said flow restricting assembly. The shutter has a larger diameter piston section provided with a top flanqe which is the part driven by the flow of the fluid. A helical spring is provided around said shutter, one end of said spring bearing on said flange, and the other end of said spring bearing on one of said hard washers. An O-ring is arranged between said flange of the shutter and the spring. Said O-ring prevents the production of noise caused by vibration of the shutter and said soft washer prevents the rattling effect at the stem portion of the shutter when the device is partially closed, and full closure is prevented by a plurality of projections provided on a shoulder formed in said shutter between the larger diameter and reduced diameter portions thereof, which projections abut against one of said hard washers forming passages for the fluid when the device is fully biased by the fluid pressure. Although this device practically solves all the problems of noise production and rattling of the prior art devices, it nevertheless still shows the drawback that derives from the fact that, at high pressures of fluid, the soft washer tends to be squeezed out of the sandwiched washer assembly, thus clogging the outlet of the tubular fitting with the consequent disabling of the whole device.